A survey for variable young stars with small telescopes: VI -- Analysis of the outbursting Be stars NSW284, Gaia19eyy, and VES263

TL;DR

This study analyzes the outburst behavior of three Be stars using multi-wavelength photometry and spectroscopy, confirming their regular outbursts and supporting the decretion disk model for Be star variability.

Contribution

It provides detailed modeling of outburst light curves, infers disk properties, and confirms the inside-out disk evolution in outbursting Be stars.

Findings

Models accurately predict burst shapes and amplitudes.

Disk sizes are 3-6 times the star's area.

Spectroscopy supports inside-out disk evolution.

Abstract

This paper is one in a series reporting results from small telescope observations of variable young stars. Here, we study the repeating outbursts of three likely Be stars based on long-term optical, near-infrared, and mid-infrared photometry for all three objects, along with follow-up spectra for two of the three. The sources are characterised as rare, truly regularly outbursting Be stars. We interpret the photometric data within a framework for modelling light curve morphology, and find that the models correctly predict the burst shapes, including their larger amplitudes and later peaks towards longer wavelengths. We are thus able to infer the start and end times of mass loading into the circumstellar disks of these stars. The disk sizes are typically 3-6 times the areas of the central star. The disk temperatures are ~40%, and the disk luminosities are ~10% of those of the central Be star, respectively. The available spectroscopy is consistent with inside-out evolution of the disk. Higher excitation lines have larger velocity widths in their double-horned shaped emission profiles. Our observations and analysis support the decretion disk model for outbursting Be stars.